Semiconductor devices are used in a large number of electronic devices, such as computers, cell phones, and others. Semiconductor devices comprise integrated circuits that are formed on semiconductor wafers by depositing many types of thin films of material over the semiconductor wafers, and patterning the thin films of material to form the integrated circuits. Integrated circuits include field-effect transistors (FETs) such as metal oxide semiconductor (MOS) transistors.
One of the goals of the semiconductor industry is to continue shrinking the size and increasing the speed of individual FETs. To achieve these goals, fin FETs (FinFETs) or multiple gate transistors are used in sub 32 nm transistor nodes. FinFETs not only improve areal density, but also improve gate control of the channel.
Unfortunately, as the fins of FinFETs become thinner and thinner, the processing steps used to fabricate the FinFETs may produce undesirable and unintended consequences. For example, the outermost fins in a FinFET may bend or bow outwardly after some thermal annealing processes such as isolation oxide curing and consolidation due to the different and non-balanced stress applied to the inner fins and outer fins of a FinFET, which changes the fin pitch between fins and degrades yield.
In addition, after etching and cleaning steps are performed critical dimensions such as fin width of inner and outer fins may vary due to environmental differences between inner fins and outer fins. The non-uniformity and mismatch between inner and outer fins will also degrade the electric performance of the FinFET.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.